Process for obtaining alkali-metal thiosulphate from solutions containing alkali-metal sulphide



Patented Dec. 29, 1925.

UNITED STATES PATNT OFICE.

FRIEDRICH RIISBEBG, OF MANNHEIM, GERMANY, ASSIGNOR TO THE FIRM RHE-NANIA VEREIN CHEMISCHER FABRIKEN A. G., OF COLOGNE, GERMANY.

PROCESS FOR OBTAINING ALKALI-METAL THIOSULPHATE FROM SOLUTIONS CON-TAINDN'G ALKALI-METAL SULPHIDE.

R0 Drawing.

To all whom it may concern:

Be it known that I, FRIEDRICH RiisBERc, a German citizen, residing atMannheim, Germany, have invented certain new and useful Improvements inProcesses for Obtaining Alkali-Metal Thiosulphate from SolutionsContaining Alkali-Metal Sulphide, of which the following is aspecification.

A corresponding application for Letters Patent was filed in Germany onOctober 19, 1921.

Sodium thiosul hate is nowadays freuently obtained rom sodium sulphideor from solutions of the manufacture of sodium sulphide by treatmentwith furnace gases. sists therein that the waste gases of this processregularly contain hydrogen sulphide in amounts of about one per cent byvolume and more.

Apart from the fact that the waste gases containing hydrogen sulphidelead to a contamination of the environs, considerable amounts ofsulphide are furthermore lost in this manner.

It has now been found, that it is possible greatly to reduce theformation of hydrogen sulphide or even to avoid such formationaltogether, if one employs the sulphurous acid required for sulphurizingthe solution of sodium suphide not in form of furnace gases but in aform as undiluted by other gases as possible, be it in form of highlyconcentrated or pure gases of sulphurous acid as are obtained in manytechnical processes or be it in form of an aqueous solution. Thereaction then ensues along with precipitation of sulphur, whereas theconcentration of the hydrogen sulphide in the waste gases keeps ongetting less and less with increasing concentration of the gasescontaining sulphur dioxide. In employing pure gases of sulphurous acidas well as sulphurous acid in solution no h (lrogen sulphide whatever isformed. T e reaction may be represented by this work- One drawback ofthe process con- Application filed May 28, 1925- Serial No. 33,492.

ing method by means of the following equation:

2Na S+3SO, =2Na S O,+S. Seeing that the precipitated sulphur in statunascendi exists in the condition of ex- In place of alkali metalsulphite, alkali metal bisulphite may also be used.

Examples.

1. A mother liquor or lye containing 540 g. Na S.9H O per litre istreated with sulphurous acid in the usual manner, one half of its volumeof a saturated solution of sodium sulphite being added simultaneously.The gas employed contains 32 per cent by volume of S0 An almostquantitive reaction results.

2. A solution containing 540 g. Na. ,S.9H O per litre is mixed with halfits volume of a solution of soda (Na CO containing 160 g. Na CO, perlitre; whereupon this mixture is treated with a gas containin 32 percent by volume of $0,. One obtains a solution of sodium thiosulphatecontaining 490 g. Na,S,O,.5H O per litre and only a trace of sulphite.

3. 1000 litres of a solution containing 480 g. Na S.9H,O per. litre "aremixed with 630 litres of a solution of sodium sulphite, containing 200g. Na SO per litre, whereupon concentrated sulphurous acid is added. Thesulphurous acid is completely absorbed. As soon as the solution gives aneutral reaction with litmus paper the reaction is finished.

4. 1000 litres of a concentrated solution of sodium sulphide containin800 of Na S.9H O per litre are imxed, with 610 litres of a solution ofsodium bisulphite containing566 g. NaHSO per litre and 2520 litres of anaqueous solution of sulphurous acid. No hydrogen sulphide is formed, noris any sulphur preci itated. The solution of sodium thiosulp ateobtained contains 320 g. of N 21 8 0 511 0 perlitrc.

What I claim and desire to secure by Letters Patent of the United Statesis:

The process of'obtaining sodium thiosulphate from solutions containingsodium sulphide, which consists in treating said solutions, in thepresence of sodium sulphite, with a gas containing thirty-two percent byvolume of sulphur dioxide.

FRIEDRICH RUSBERG.

